Dynamics of large-scale solar-wind streams obtained by the double superposed epoch analysis. 4. Helium abundance

TL;DR

This study analyzes the average helium abundance in large-scale solar wind streams over four decades, revealing its variations across different solar wind structures and its correlation with plasma beta, offering insights into CME formation conditions.

Contribution

It provides the first detailed analysis of helium abundance Nα/Np in relation to plasma beta in various solar wind structures, extending previous work on solar wind parameters.

Findings

Helium abundance is higher in fast streams than in slow streams.

Nα/Np correlates with plasma beta in CIRs and Sheaths, and anti-correlates in ICMEs.

The Nα/Np vs. beta relationship is stronger in magnetic clouds, indicating potential as a CME formation indicator.

Abstract

This work is a continuation of our previous articles (Yermolaev et al. in J. Geophys. Res. 120, 7094, 2015; Yermolaev et al. in Solar Phys. 292, 193, 2017; Yermolaev et al. in Solar Phys. 293, 91, 2018), which describe the average temporal profiles of interplanetary plasma and field parameters in large-scale solar-wind (SW) streams: corotating interaction regions (CIRs), interplanetary coronal mass ejections (ICMEs including both magnetic clouds (MCs) and ejecta), and sheaths as well as interplanetary shocks (ISs). In this work we analyze the average profile of helium abundance N{\alpha}/Np for interval of 1976-2016. Our results confirm main early obtained results: N{\alpha}/Np is higher in quasi-stationary fast streams than in slow ones; it slowly changes in compression regions CIRs and Sheaths from values in undisturbed solar wind to values in corresponding type of piston (HSS or ICME); in Ejecta it is closed to abundance in undisturbed streams and it is maximal in MCs. We obtained for first time that N{\alpha}/Np correlates with plasma {\beta}-parameter in compression regions CIRs and Sheaths and anti-correlates in ICMEs. The N{\alpha}/Np vs. {\beta} dependence is stronger in MCs than in Ejecta and may be used as an indicator of conditions in CME formation place on the Sun.